Dual fuel grid burner

ABSTRACT

A grid burner suitable for combustion of either gas or liquid fuel. The gas fuel supply manifold surrounds and shields the liquid fuel manifold which is supported by tubular expansion coils connected to the fuel nozzles. Recirculation of liquid fuel through an inner pipe prevents overheating. Gutter-type flameholders aid in flame stabilization.

United States Patent [72] Inventors RobertE.Kegan [56] References Cited UNITED STATES PATENTS 2,497,476 2/1950 Stadler Boxford, Mass.;

Frank A. Underwood, Akron, Ohio; General Electric Company pp No 73,411 2,918,966 12/1959 Ferguson...................... [22] Filed Primary Examiner-Carroll B. Dority, Jr.

Attorneys-William C. Crutcher, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. Forman Sept. 18,1970 [45] Patented Jan. 4, 1972 [54] DUAL FUEL GRID BURNER ABSTRACT: A grid burner suitable for combustion of either gas or liquid fuel. The gas fuel supply manifold surrounds and shields the liquid fuel manifold which is supported by tubular expansion coils connected to the fuel nozzles. Recirculation of liquid fuel through an inner pipe prevents overheating. (nuttertype flameholders aid in flame stabilization.

1.0 1 MSNMS nB92 1 U9 "3 M132 4 2 3 9 2 mu m m m3 m m m mimm u" NH mm "u n u m mm F m mm 2. m mm m m I a m M I n u D m m 4 m e n m m I" f. o M d C M 8 U I .F 1.. .1] 2 10 D "DU SHEET 1 [IF 2 INVENTORS ROBERT E. KEGAN, FRANK A. UNDERWOOD THEIR ATTORNEY.

mcmcnm we $632,286

SHEET 2 OF 2 l INVENTORSI ROBERT E. KEGAN, FRANK A. UNDERWOOD,

BY 4). 6 Mm THEIR ATTORNEY.

DUAL FUEL GRID BURNER BACKGROUND OF THE INVENTION This invention relates generally to a dual fuel grid burner and more particularly to a shielded fuel manifold assembly suitable for alternate use of gaseous or liquid fuel as well as for pressure atomization of liquid fuels.

A grid burner allows supplementary firing of air or of vitiated waste heat gases such as hot gas turbine exhaust in order to raise the temperature of the gas for industrial use or for the purpose of generating steam in a heat recovery steam generator. The use of multiple combustion nozzles in a grid burner has been suggested in the prior art such as U.S. Pat. No. 3,457,902 to Gjerde. The burner elements may be of the type suitable for burning gaseous fuel with stabilizing flame holders to admit stabilizing air such as disclosed in U.S. Pat. No. 3,405,921 to Rohrs. Also, burners are well known in the art which are suitable for burning liquid fuel such as U.S. Pat. NO. 2,333,531 to Ferguson. The foregoing cited patents are only exemplary of many in this field.

Although the burning of gaseous fuel presents no great problem, multiple liquid burners are subject to problems of uniform fuel distribution to the burner nozzles. Overheating of the oil as it flows through the distribution conduit or manifold can produce a vapor lock or a coking problem when the liquid fuel is exposed to the radiant heat from the burners or the hot waste heat gases.

Where a large tumdown ratio is necessary (ratio of maximum to minimum firing rate), the fuel is prone to boiling and starving of the nozzles at the far end of the supply manifold at low fuel flow rates. This produces coking and clogging of the oil nozzles and an unfavorable effect on burner perforrnance.

Accordingly, one object of the present invention is to provide a dual fuel grid burner with an improved fuel manifold assembly suitable for supplying either liquid or gaseous fuel to the burner nozzles.

Another object of the invention is to provide an improved liquid fuel supply manifold suitable for atomization of the liquid fuel and having provision for improved fuel distribution along the multiple nozzles.

Still another object of the invention is to provide an improved dual fuel burner with a shielded liquid fuel manifold andprovisions for thermal expansion of the parts relative to one another.

DRAWING The invention both as to organization and method of practice, together with further objects and advantages thereof, will best be understood by reference to the following specification, taken in connection with the accompanying drawings, in which:

FIG. I is a plan view of the grid burner showing the arrangement of the burner elements and the flameholders,

FIG. 2 is a horizontal view, partly in section, of a single burner element,

FIG. 3 is a cross section taken through the burner element at one fuel nozzle along III-III of FIG. 2, and

FIG. 4 is a cross section through the fuel nozzle taken along lines IV-IV of FIG. 3.

SUMMARY OF THE INVENTION Briefly stated, the invention is practiced by arranging a plurality of dual fuel nozzles along the gas manifold. A liquid manifold is disposed within the gas manifold and supported by tubular expansion coils carrying liquid from the liquid manifold to the fuel nozzle. A recirculation pipe is disposed within the liquid manifold. The gas manifold can also be employed to supply fluid for pressure atomization of the liquid fuel.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of the drawing, the grid burner comprises a rectangular open frame 1 having spaced cross members 2 and longitudinal angle members 3 supporting the burner elements 4. The individual burner elements, here six in number, are inserted from opposite ends and attached by flange plates 5 to the frame end members 6. Each burner element 4 is supplied with a gas fuel supply pipe 7 and a liquid fuel supply pipe 8, although, as will be later explained, gas supply pipe 7 can also be employed for introduction of steam or air for pressure atomization. A liquid recirculating pipe 9 is connected to a pipe (not shown) leading back to the fuel tank or pump inlet.

Each burner element 4 includes guttertype flameholders 10 with sliding expansion joints 11. A group of longitudinally spaced nozzles 12 extend along the top of a gas manifold pipe 13 and are supported thereby. The entire base of frame I is covered by a grid of stainless steel wire mesh 14 to straighten the flow of the incoming air or waste heat turbine exhaust if necessary.

In one intended application of the present invention, the frame 1 is interposed in a duct carrying combustionsupporting exhaust gas from a gas turbine and is used to heat the gas in a process known as supplementary firing" as the gas travels toward a heat recovery steam generator. These details are not shown, but a typical system may be seen by reference to U.S. Pat. No. 3,443,550 issued to H. F. May and J. M. Kovacik on May 13, I969 and assigned to the present assignee.

Referring now to FIG. 2 of the drawing, which is an enlarged view of one of the burner elements 4, the burner element gas manifold pipe 13 is closed ofl at one end by a plug 15 and at the other end by a plate 16. Pipe 13 is welded to flange 5 and surrounded by a collar 17 inside the flange in order to provide support in the grid frame end wall. Gaseous fuel, such as natural gas from an external source is led to supply pipe 7 and enters through a side connection at 18. Along its length, the gas manifold pipe 13 is also supported by an angle member 3. The latter also supports the divergent V- type walls of the fiameholder 10 by means of spaced brackets 19 (see also FIG. 3).

Fuel nozzles 12 are spaced along the top of the gas manifold pipe 13 by welding into suitable openings. Gas enters the nozzles 12 through distribution holes 20. Liquid enters the fuel nozzles via tubular expansion coils 21.

The expansion coils 21 preferably are helical and surround a liquid fuel manifold pipe 22 as indicated. Although they could be of a sinuous shape, a helix is much preferred in terms of expansion ability and space saving. It should be noted from FIG. 2 that the number of turns in the helical coils increase along the length of the burner toward the center of the grid, so as to accommodate greater relative differences in expansion and. contraction when going from the grid frame end walls.

The liquid fuel manifold pipe 22 is disposed within the gas manifold 13 so that it is completely shielded thereby. One end of the liquid manifold 22 is closed off 'by means of a cap 23 and the other end is connected by means of a T- fitting to the liquid supply pipe 8 which receives liquid fuel from an external source. The tubular expansion coils spaced along the liquid manifold 22 are connected to the interior of the liquid pipe 22 at one end and connected to the fuel nozzle 12 at the other. These serve both to support the liquid manifold pipe from the fuel nozzle assemblies, as well as to provide for longitudinal thermal expansion of the liquid pipe 22 relative to the gas manifold 13.

Disposed inside the liquid manifold 22 is a recirculation pipe 24 which is open at one end at 25 to allow for return flow of unused liquid. The recirculation pipe 24 extends the full length of pipe 22 and the recirculated liquid leaves via outlet Referring now to FIG. 3 of the drawing, which is a cross section through the burner element, the details of the nozzle assembly will be seen as well as the configuration of the already known guttertype flameholder 10. The flameholder may include slots a for admission of air or exhaust gas to stabilize the flame. A perforated screen 37 rests on nozzles 12 and is secured by retainers 38. Screen 37 extends across the space between the flameholder aperture and also extends the length of burner element 4. The perforations in screen 37 admit primary air for combustion as shown by the arrows.

Many kinds of fuel nozzles are suitable for nozzle 12, which is shown herein merely as a typical design. Nozzle 12 includes a retainer 26 which is welded into the gas manifold pipe 13 and includes the gas inlet holes 20. A flowmetering swirler insert 27 is threaded into the retainer 26 and a nozzle cap 28 is threaded onto the swirler insert. Nozzle retainer 26 also includes a nozzle stem retainer 29 which is connected at one end to the tubular expansion coil 21. A conventional liquid fuel orifice stem and filter 30 is threaded into the stem retainer 29. An annular passage 31 between the nozzle cap and the liquid fuel orifice provides for egress of the gaseous fuel when buming gas alone or for atomizing fluid when operating as an atomizing liquid nozzle.

The FIG. 4 cross section through the nozzle shows that the flowmetering and swirler insert 27 is provided with tangential entry holes 32 to provide a proper crosssectional area for fuel metering and slanted to produce a swirl to the entering gas (or atomizing fluid). The swirl produces a shorter flame length for the gaseous fuel or atomized fuel departing at annular passage 31. The nozzle parts are all threaded so they can be removed for cleaning or adjustment.

- OPERATION The operation of the invention will apparent from the following description. When buming gaseous fuel, the liquid manifold 22 is empty, having been purged by steam or air, and is isolated by an external valve (not shown). The gaseous fuel flows along gas manifold 13 and through the distribution ports 20. Metering and swirl are provided as it flows through tangential passages 32 and the fuel burns as it leaves the annular passage 31. Combustion takes place in the region above the flameholder 10 as oxygen is derived from the turbine exhaust or fresh air flowing past the burner elements. Stabilization of flame is provided by exhaust or air flowing through screen 10b and 10a in the flameholder.

When burning liquid fuel, liquid is introduced through inlet pipe 8 into liquid manifold 22 where it flows along the manifold and out through the various expansion coil pipes 21 into the individual nozzles. An important feature of the present invention is the thermal shielding of the liquid manifold 22 by the gas manifold 13, which shielding is provided both by the surrounding manifold pipe itself as well as the gas space inbetween the pipes. The gas manifold 13 is either empty or may, in some cases, be full of atomizing air or steam under pressure. In either case, shielding from radiant heat and uniform temperature distribution of the liquid manifold pipe 22 are best provided.

When firing liquid fuel at high temperatures, atomization is not required and the liquid fuel simply sprays from the nozzle orifice 30 and combustion takes place in the flameholder in the presence of the combustionsupporting exhaust gas as before.

If atomization is required, it is only necessary to introduce the atomizing fluid into gas manifold 13 via inlet pipe 7 by means of suitable valving. The atomizing fluid is metered and given a tangential swirl by slots 32 which aids in mixing and atomizing the liquid fuel leaving orifice 30. If air is used for atomization, it acts as a barrier for heat transfer from the gas manifold pipe 13, thereby shielding the liquid manifold pipe and reducing problems of the prior art. If steam is used, depending upon the liquid fuel, increased bypass flow through tube 24 can prevent the fuel from overheating.

An important aspect of the present invention is the inner recirculating pipe 24. It is approximately sized so that a substantial quantity of unused liquid returns through the open end 25 of the recirculation pipe. This counterflow arrangement tends to distribute the temperature of the liquid uniformly within the liquid manifold the prevent boiling. Also, since substantial liquid is recirculated, high tumdown ratios are possible without starving the liquid nozzles at the far end of the manifold or overheating the liquid.

Another feature of the present invention is the use of the expansion coils 21 to provide for a relative thermal expansion in a longitudinal direction between the liquid pipe and the gas pipe. It will be appreciated that under the two different options of fuel supply, as well as during transient temperature changes, relative movements will take place between the two longitudinal pipes, and the relative longitudinal positions of the pipes are compensated for by expansion and contraction of the expansion coils supporting the liquid pipe. The use of a greater number of turns per coil toward the center of the grid accommodates the greater relative movements in that locatron.

Thus it can be seen that an improved dual fuel grid burner has been provided which greatly facilitates the supply of either liquid or gaseous fuel to the dual nozzles, as well as providing for optional fluid atomization of liquid fuels with no further changes except through manipulation of external valving. The improved shielding and support arrangement for the liquid manifold pipe as well as the provisions of liquid recirculation, serve to reduce many of the problems of the prior art.

While there has been disclosed what is herein considered to be the preferred embodiment of the invention, other modifications will occur to those skilled in the art, and it is desired to include in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a grid burner having a plurality of spaced burner elements and adapted for flow of a combustionsupporting gas across said burner elements to be heated thereby, the improvement comprising:

a burner element having a plurality of fuel nozzles spaced along said element, each nozzle being adapted for introduction of gas or liquid fuels to said nozzle at separate gas and liquid inlets, and arranged for combustion of either of said fuels,

a gas manifold conduit supporting said nozzles and communicating with said gas inlets,

a liquid manifold conduit disposed within and extending along the length of said gas manifold conduit so as to be shielded thereby,

a plurality of tubular expansion coils arranged to support the liquid manifold, each with one end connected to said liquid manifold and the other end connected to said liquid inlet of one of said nozzles, whereby said expansion tubes supply liquid to the nozzles and support the shielded liquid manifold for thermal expansion and contraction relative to the gas manifold.

2. The combination according to claim 1 further including:

a source of liquid fuel connected to one end of said liquid manifold conduit,

means closing off the other end of the liquid manifold conduit, and

a liquid recirculation pipe disposed inside the liquid manifold and being adapted to return unused liquid fuel from the closedoff end and along the length of said liquid manifold in heat transfer relationship therewith, whereby tendency toward nozzle starving" and boiling of the liquid fuel at said closedoff end is reduced.

3. The combination according to claim 1 and further includan open grid burner frame,

means arranged to support said gas manifold along its length in said grid burner frame,

a guttertype flameholder with divergent walls extending above said gas manifold and having first openings to admit the ends of said nozzles and second openings adjacent said first openings arranged to admit said combustionsupporting gas and to stabilize the-flame, and

bracket means connected between the flameholder and said a plurality of spaced burner elements extending into the supporting means and arranged to support the frame and supported on one end by the frame sidewalls, fiameholder therefrom. a grid mesh covering the bottom of the frame below said 4. The combination according to claim 3, wherein said burner elements to straighten the flow to the burner elesecond openings are opposed slots defined by said flamen- 5 ments, holder walls adjacent each of said nozzles. each of said burner elements comprising:

5. The combination according to claim 3, wherein said a gas manifold pipe extending into the frame and closed second openings are defined in a perforated screen supported off at its inner end, by said nozzles and forming an extension of said flameholder a p u ality of fuel nozzles spaced along said gas manifold walls. 10 pipe, each of said nozzles being adapted for burning of 6. The combination according to claim 1, wherein each of gas us of liquid fuel and having separate gas inlet said fuel nozzles comprises: ports and liquid inlet ports,

a nozzle retainer fixedly mounted in said gas manifold and a q "l PP dlsPo-sed l and extendlflg defining first ports admitting gas to the retainer, fllong Sald gas mamfold P p and bmng closed Off flowmetering swirler means mounted coaxially within said 'P i retainer and defining second ports sized and arranged to a plurality of hellcal tulmlar expansion coll-S dfsposed meter h gas d to impart a i l to h gas, around said liquid manifold pipe and each having one liquid orifice means mounted coaxially within said flowmeend connected a f l inlet and the Othel: end tering swirler means and connected to one end of a said connecfed to Said P p 50 to comm'umcaie tubular expansion coil to supply liquid to the orifice. tlferewlth and p y llquld fuel While Supporting 531d 7. The combination according to claim 1, wherein each of P P i I I i said tubular expansion coils is in the shape of a helix surrounda hqulld reclrculallon P'P dlsposed Inside the llquld ing said liquid manifold and secured at one end in the top manifold 9 and e adapted to return unused fuel thereof, the number of turns in said coils increasing along the from the closed off and burner element toward the center of the grid. a yp flamFholdel' exiefldmg sflld g 8. A dual fuel grid burner for supplementary firing of a commamfold and havmg first Openings to {ldmlt 531d bustiomsupporting exhaust gas comprising: zles and second openings to admit said combustiona supporting frame having sidewalls forming portions of a supportmg exhaust duct carrying said exhaust gas, 

1. In a grid burner having a plurality of spaced burner elements and adapted for flow of a combustion-supporting gas across said burner elements to be heated thereby, the improvement comprising: a burner element having a plurality of fuel nozzles spaced along said element, each nozzle being adapted for introduction of gas or liquid fuels to said nozzle at separate gas and liquid inlets, and arranged for combustion of either of said fuels, a gas manifold conduit supporting said nozzles and communicating with said gas inlets, a liquid manifold conduit disposed within and extending along the length of said gas manifold conduit so as to be shielded thereby, a plurality of tubular expansion coils arranged to support the liquid manifold, each with one end connected to said liquid manifold and the other end connected to said liquid inlet of one of said nozzles, whereby said expansion tubes supply liquid to the nozzles and support the shielded liquid manifold for thermal expansion and contraction relative to the gas manifold.
 2. The combination according to claim 1 further including: a source of liquid fuel connected to one end of said liquid manifold conduit, means closing off the other end of the liquid manifold conduit, and a liquid recirculation pipe disposed inside the liquid manifold and being adapted to return unused liquid fuel from the closed-off end and alonG the length of said liquid manifold in heat transfer relationship therewith, whereby tendency toward nozzle ''''starving'''' and boiling of the liquid fuel at said closed-off end is reduced.
 3. The combination according to claim 1 and further including: an open grid burner frame, means arranged to support said gas manifold along its length in said grid burner frame, a gutter-type flameholder with divergent walls extending above said gas manifold and having first openings to admit the ends of said nozzles and second openings adjacent said first openings arranged to admit said combustion-supporting gas and to stabilize the flame, and bracket means connected between the flameholder and said supporting means and arranged to support the flameholder therefrom.
 4. The combination according to claim 3, wherein said second openings are opposed slots defined by said flamenholder walls adjacent each of said nozzles.
 5. The combination according to claim 3, wherein said second openings are defined in a perforated screen supported by said nozzles and forming an extension of said flameholder walls.
 6. The combination according to claim 1, wherein each of said fuel nozzles comprises: a nozzle retainer fixedly mounted in said gas manifold and defining first ports admitting gas to the retainer, flow-metering swirler means mounted coaxially within said retainer and defining second ports sized and arranged to meter the gas and to impart a swirl to the gas, liquid orifice means mounted coaxially within said flow-metering swirler means and connected to one end of a said tubular expansion coil to supply liquid to the orifice.
 7. The combination according to claim 1, wherein each of said tubular expansion coils is in the shape of a helix surrounding said liquid manifold and secured at one end in the top thereof, the number of turns in said coils increasing along the burner element toward the center of the grid.
 8. A dual fuel grid burner for supplementary firing of a combustion-supporting exhaust gas comprising: a supporting frame having sidewalls forming portions of a duct carrying said exhaust gas, a plurality of spaced burner elements extending into the frame and supported on one end by the frame sidewalls, a grid mesh covering the bottom of the frame below said burner elements to straighten the flow to the burner elements, each of said burner elements comprising: a gas manifold pipe extending into the frame and closed off at its inner end, a plurality of fuel nozzles spaced along said gas manifold pipe, each of said nozzles being adapted for burning of gaseous of liquid fuel and having separate gas inlet ports and liquid inlet ports, a liquid manifold pipe disposed within and extending along said gas manifold pipe and being closed off at its inner end, a plurality of helical tubular expansion coils disposed around said liquid manifold pipe and each having one end connected to a fuel nozzle inlet and the other end connected to said liquid pipe so as to communicate therewith and supply liquid fuel while supporting said pipe, a liquid recirculation pipe disposed inside the liquid manifold pipe and being adapted to return unused fuel from the closed-off end, and a gutter-type flameholder extending above said gas manifold and having first openings to admit said nozzles and second openings to admit said combustion-supporting exhaust gas. 